Perturbations which block the neural activation of salivary gland secretion lead to atrophy and the concomitant loss of cells expressing exocrine cell phenotypes. Thus, phenotypic exocrine cell expression in adult glands is dependent, in part, upon mechanisms regulated by neurotransmitters released by autonomic nerves during activation of secretion. Elucidation of these neural mediated mechanisms will provide insights into efforts to induce and maintain expression of exocrine cell phenotypes of implanted (or transplanted) salivary cells (or tissue) as part of cell-based therapies to enhance exocrine function of damaged salivary glands. Unfortunately, advancement in our understanding of these mechanisms is hindered by the absence of appropriate in-vitro model systems such as highly differentiated cell lines or primary cultures of salivary exocrine cells. Our laboratory is focused on the regulation of salivary mucous glands. specifically rat sublingual glands. These glands. in contrast to other salivary glands. receive predominantly parasympathetic nerves which stimulate both fluid and exocrine secretion of acinar mucous cells through activation of muscarinic cholinergic receptors. In a preliminary study, chronic systemic administration of muscarinic antagonist resulted in mucous gland atrophy with the apparent selective diminution of expression of the mucous cell phenotype. We have since developed a protocol to deliver antagonist directly to sublingual glands which will provide the unique opportunity to study muscarinic mediated mechanisms controlling maintenance of mucous cell phenotypic expression in adult glands. In addition, removal of antagonist after diminishment of mucous cell phenotypic expression is expected to initiate mechanisms to regenerate normal mucous acinar structures, in-vivo. We therefore propose to initially evaluate this model system. Specifically. we plan to apply morphometric and biochemical criteria to l) determine changes with time in the expression of mucous. serous demilune. and ductal cells of rat sublingual glands in response to chronic atropine treatment; and to 2) determine the regenerative capacity of each cell type upon removal of antagonist. Future information derived from studies using this model may ultimately be used to treat xerostomic patients with new cell-based therapies such as genetically engineered transplant tissue or progenitor cells designed to continually express functional exocrine cell phenotypes.